1. Field of the Invention
The present invention relates to an ink jet printing apparatus, an ink jet printing method, and a non-transitory computer-readable storage medium.
2. Description of the Related Art
Known ink jet printing apparatuses include an ink jet printing apparatus that uses a printing head having a substrate on which a printing element array having a plurality of printing elements that generate thermal energy used to eject ink are arranged in an array direction. In this apparatus, the printing elements are driven while the printing head is moved in such a manner as to scan a printing medium, whereby thermal energy is given to ink near the printing elements and ink is ejected onto the printing medium to form an image.
In such an ink jet printing apparatus, it is known that there is a case in which ejection volume is decreased or ejection fails when the temperature of ink at the time of ejecting the ink is low. When such a phenomenon is generated, the quality of a printed image is degraded. To cope with this problem, Japanese Patent Laid-Open No. 4-22727 discloses a technology in which by providing a temperature adjustment heater (hereinafter, also called a sub-heater or a heating element) for heating ink in the vicinity of printing elements on a substrate, ink is heated through short-pulse heating control, in which heating is performed by providing the printing elements with driving pulses short enough not to allow ink to be ejected, together with sub-heater control using the sub-heater. It is stated in the above document that heating to a target temperature is performed through control of short-pulse heating, which has a relatively high heating capability, and the temperature is then maintained through control of sub-heater heating having a relatively low heating capability.
On the other hand, there may be a case where a temperature distribution in which temperature changes in accordance with the positions of the printing elements in the array direction is generated, even when uniform thermal energy is applied to ink in the vicinity of the printing elements within the printing element array. The higher the temperature, the higher the ejection volume and, hence, the ejection volume varies among the printing elements in accordance with this temperature distribution. This may result in generation of uneven color density in a printed image. Regarding this problem, it is stated in Japanese Patent Laid-Open No. 4-250057 that the above-described temperature distribution is reduced by providing a plurality of sub-heaters and temperature sensors in the substrate in accordance with the positions in the array direction and by driving the sub-heaters partially on the basis of the temperatures detected by the temperature sensors.
However, it turned out that a decrease in image quality due to variations in the ejection volume may not be sufficiently suppressed even when the method disclosed in Japanese Patent Laid-Open No. 4-22727 is employed, if a temperature distribution in which temperature changes in accordance with the positions of the printing elements in the array direction is generated when uniform thermal energy is applied to the printing element array. In addition, it turned out that the durability of a printing head may decrease.
Hereinafter, this problem will be described in detail.
Note that the case described below is a case in which the temperature of the end portions of the printing element array in the array direction is more likely than that of the center portion to be decreased due to heat dissipation.
FIGS. 1A and 1B are diagrams for respectively illustrating changes in temperature at the end portions and center portion of the printing element array, and a temperature distribution, in the case where heating to a target temperature is performed only through control of short-pulse heating which has a relatively high heating capability. Note that the target temperature is 40° C. in the case described here. The temperature in the apparatus near the printing head within the inkjet printing apparatus is 25° C.
FIG. 1A is a diagram illustrating changes in temperature at the end portions and center portion of the printing element array in the array direction in the case where heating to a target temperature is performed only through short-pulse heating. Note that, in FIG. 1A, the solid line represents a change in temperature at the center portion of the printing element array and the broken line represents a change in temperature at the end portions of the printing element array. Since the temperature of ink is approximately the same as that of the substrate, the substrate temperature is obtained and used as the temperature of ink.
As described above, when the printing elements in the printing element array are uniformly heated, the substrate temperature at the center of the printing element array is likely to increase more than the substrate temperature at the end portion, due to heat dissipation at the end portions of the printing element array. Hence, at the center portion, the target temperature of 40° C. is reached at a time point when elapsed time T=t1 (0<t1<0.5) seconds, after short-pulse heating was started. At this time point, the substrate temperature at the end portions is about 32° C.
At a time point when the elapsed time T=t2 (1.5<t2<2) seconds, while short-pulse heating has been continued, the temperature at the end portions reaches 40° C., which is a target temperature. At this time point, the temperature at the center portion of the substrate has reached 60° C., because heating has been continued for additional (t2−t1) seconds after the target temperature was reached.
FIG. 1B is a diagram illustrating the substrate temperature distribution within the printing element array after the short-pulse heating has been performed. Note that, in FIG. 1B, the solid line represents the temperature distribution observed t2 seconds after the short-pulse heating was started, and the broken line represents the temperature distribution observed t1 seconds after the short-pulse heating was started.
At a time point when the elapsed time T=t1 seconds, at which the substrate temperature at the center of the printing element array reaches the target temperature, the substrate temperature at the end portions is lower than the target temperature, as described above. Hence, in the case in which ink ejection is performed at a time point when the elapsed time T=t1 seconds, the ejection volume may be decreased or ejection may not be performed in the printing elements at the end portions, since the substrate temperature at the end portions has not reached the target temperature.
On the other hand, at a time point when the elapsed time T=t2, at which the substrate temperature of the end portions of the printing element array reaches the target temperature, the substrate temperature at the center portion considerably exceeds the target temperature. Note that such a phenomenon, in which the target temperature is considerably exceeded during heating, is also called an overshoot phenomenon. As a result, when ink is ejected, there may be a case in which the volume of ink ejected from printing elements at the center portion is increased. Further, in the case in which the ejection port member provided in such a manner as to face the printing elements is formed of a resin or the like, the ejection port member may gradually be deformed due to a thermal stress produced by this overshoot phenomenon. This deformation of the ejection port member may cause a decrease in the durability of the printing head.
The above-described variations in the ejection volume and the decrease in the durability of the printing head may occur also in the case where short-pulse heating and sub-heater heating are used together.
FIG. 2A is a diagram illustrating changes in temperature respectively at the end portions and center portion of the printing element array in the array direction in the case where short-pulse heating and sub-heater heating are started at the same time. FIG. 2B is a diagram illustrating the temperature distributions of the substrate at a time point when the elapsed time T=t1 at which the center portion has reached a target temperature and at a time point when the elapsed time T=t2 at which the end portion has reached a target temperature, after the start of heating, illustrated in FIG. 2A.
As can be seen from FIG. 2B, also in the case where the short-pulse heating and sub-heater heating are started at the same time, a non-uniform temperature distribution may be generated to some extent in some cases. Hence, a decrease in durability due to variations in the ejection volume or an overshoot phenomenon may be generated.